In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipment (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, which may also be referred to as a beam or a beam group, with each service area or cell area being served by a radio network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a “NodeB” or “eNodeB”. A service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the wireless communication device within range of the radio network node.
A Universal Mobile Telecommunications System (UMTS) is a third generation (3G) telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network.
3GPP 5G New Radio (NR) is the wireless standard that will become the foundation for the next generation of mobile networks. FIG. 1 depicts an overview of the downlink (DL) based active mode mobility solution proposed for 3GPP 5G NR.
As shown in FIG. 1, a UE is served by the leftmost network node, i.e. the serving node 1, but is traveling in the direction towards the rightmost network node 2, depicted by the dashed arrow in the figure. The UE uses the best “home MRS” (Mobility Reference Signal) for coarse timing estimation and radio link quality monitoring and failure detection, denoted by the dot filled oval in the figure. Alternative names instead of MRS may be Active mode synch signal (AMSS), active mode reference signal or Channel State Information Reference Signal (CSI-RS).
In addition, the UE monitors a sparse periodic MRS from the serving network node 1 and compares it with similar periodic and sparse MRSs from potential target network nodes, e.g. the network node 2. When a target network node becomes relevant for a more detailed handover procedure additional dynamically configured home MRSs from the serving network node 1 and dynamically configured away MRSs from the target network node, e.g. the network node 2, may be activated.
The final handover decision is taken by the network and it is based on UE reports containing measurements of home MRSs and away MRSs.
An example of a proposed system information acquisition for 5G NR is depicted in FIG. 2. In the example each network node, which may also be referred as RBS, eNB, gNB, transmission and reception point (TRP), transmits a synchronization signals or a system signature signal (SS or xSS). Together with the SS each network node also transmits a physical broadcast channel (PBCH) containing some of the minimum system information that the UE need to access the network. This part of the minimum system information is denoted as master information block (MIB) in the figure. The transition of SS and the physical broadcast channel (PBCH) containing the MIB is denoted with dot filled ovals in the figure.
By reading the MIB the UE receives information on how to receive the system information block (SIB) table. The SIB table may be transmitted using a broadcast format such as single frequency network (SFN) transmission and it is depicted with a dashed oval in the figure.
In addition to the minimum system information that is periodically broadcasted by the SS+MIB and in the SIB-table the UE may receive other system information e.g. by a dedicated transmission after initial access is established, depicted with an oval with label “Additional SI transmission” in the figure.
With 5G, the possibility to beamform data transmissions enable a UE to travel far away from its serving network node with a maintained radio quality. This means that the UE could move out of the SS broadcast area, or system area, of the serving network node, but still be connected to the serving network node. An example is shown in FIG. 3.
FIG. 3 depicts a UE served by a data beam, i.e. an active mode beam, from one network node BS1, but with System Information coverage from another network node BS3.
When the UE goes to Idle or inactive or any kind of sleeping state mode, it will find SS3 and camp on BS3. If the UE wants to go back to active mode within a given time window, it is likely that the same beam, the data beam, from BS1 will still be the best beam. However, since the UE can only hear SS3, it will first connect to BS3, and then perform a handover to BS1. When the UE connects to BS3, the UE context will not be known there.
Without knowledge of which active mode beams and which idle mode cells, i.e. network nodes with SS broadcast areas, that are neighbors, these situations will result in degraded performance. For example, a UE may be toggling between active mode and idle mode in a location where active beam and idle mode cell coverage is provided by different network nodes or base stations.